The Mongols prized their horses primarily for the advantages they offered in warfare. In combat, the horses were fast and flexible, and Chinggis Khan was the first to capitalize fully on these strengths. After hit-and-run raids, for example, his horsement could race back and quickly disappear into their native steppes. Enemy armies from the sedentary agricultural societies to the south frequently had to abandon their pursuit because they were not accustomed to long rides on horseback and thus could not move as quickly.
The Mongols had developed a composite bow made out of sinew and horn and were skilled at shooting it while riding, which gave them the upper hand against ordinary foot soldiers. With a range of more than 350 yards, the bow was superior to the contemporaneous English longbow, whose range was only 250 yards. A wood-and-leather saddle, which was rubbed with sheep's fat to prevent cracking and shrinkage, allowed the horses to bear the weight of their riders for long periods and also permitted the riders to retain a firm seat. [And] a sturdy stirrup enabled horsemen to be sturdier and thus more accurate in shooting when mounted.
A Chinese chronicler recognized the horse's value to the Mongols, observing that "by nature they [the Mongols] are good at riding and shooting. Therefore they took possession of the world through this advantage of bow and horse."
text above excerpted from "All the Khan's Horses," by Morris Rossabi (in Natural History, October 1994 / Reprinted with permission from the author)] click here for full text [PDF]